The present invention relates generally to propfans used in propulsion systems, and more particularly to fan blades in small, high speed propfan turbine engines.
Prior art turbine fan blades have generally been constructed entirely of metal which is cast or machined into an assembly to be powered by an engine drive mechanism. However, an all-metallic blade has the drawbacks of the blade tending to be heavy. The blade can also have a relatively low modulus/density ratio leading to reduced aerodynamic performance due to blade tip deflections and blade untwist.
One solution to this problem is to provide a fan blade of composite fiber construction. A composite fan blade has a lower weight and a greater modulus/density ratio than a metal blade. Reduced weight in a gas turbine engine component increases flight time and lowers inertial response time. A higher modulus/density ratio improves aerodynamic performance.
The strength of the composite material derives from the fibers utilized therein. A composite design must optimize the orientations of the fiber loading in order to achieve maximum benefit of the composite design. However, the problem inherent with a fan blade arrangement is the fan blade requires strength in the radial direction, and the fan support disk requires strength in the tangential direction. An integral composite fan design would thus require a very complicated three-dimensional fiber weave in order to tailor the fiber orientations to the structural requirements of the fan blade and support disk.